<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        body {
            background-color: #bbb;
        }

        #canvas {
            background-color: #fff;
        }
    </style>
</head>

<body>
    <canvas id="canvas" width="400" height="400"></canvas>
</body>
<script src="./utils.js"></script>
<script>
    window.onload = () => {
        var canvas = document.getElementById("canvas")
        var context = canvas.getContext('2d')
        var mouse = utils.captureMouse(canvas)
        var x0 = 100, y0 = 200, x2 = 300, y2 = 400

        canvas.addEventListener('mousedown', function (e) {
            context.clearRect(0, 0, canvas.width, canvas.height)
            var x1 = mouse.x * 2 - (x0 + x2) / 2,
                y1 = mouse.y * 2 - (y0 + y2) / 2
            context.beginPath()
            context.moveTo(x0, y0)
            context.quadraticCurveTo(x1, y1, x2, y2)
            context.stroke()
        }, false)
    }
</script>

</html>